1. Field of the Invention
Embodiments of the present invention relate generally to medical devices and, more particularly, to devices and methods used in anchoring sutures, e.g., during surgeries involving repair of rotator cuff tendon.
2. Description of the Related Art
In surgeries involving repair of a rotator cuff tendon that has been detached from the humeral head, the tendon must be artificially pressed against the humeral head in order to allow the tendon to naturally re-attach to the underlying bone over time. FIGS. 1 and 2 illustrate a prior art technique for repairing a rotator cuff tendon that has been detached from the humeral head.
FIG. 1 schematically illustrates a rotator cuff tendon 101 secured to a humeral head 102 of a humerus 100 by a plurality of suture anchors 103. Suture anchors 103 are positioned so that sutures 104, which are sewn into rotator cuff tendon 101, position the tendon against region 105 of humeral head 102, where region 105 approximates the original anatomic attachment location of rotator cuff tendon 101. In this way, rotator cuff tendon 101 will grow onto region 105, forming a new bond between rotator cuff tendon 101 and humeral head 102. Issues associated with the use of the technique illustrated in FIG. 1 include anchor displacement from the supporting bone, and the availability of only a limited number of sutures for securing rotator cuff tendon 101 to humeral head 102.
FIG. 2 schematically illustrates one example of suture anchor 103 known in the art for attaching the rotator cuff tendon. Suture anchor 103 is positioned in a cylindrical hole 201 formed into the surface 202 of humeral head 102 illustrated in FIG. 1. As illustrated, suture anchor 103 is a wedge-shaped device configured for permanent installation into cylindrical hole 201, where suture anchor 103 can be inserted into cylindrical hole 201 with a pusher rod or other device. Because suture anchor 103 is wedge-shaped, suture anchor 103 is not displaced by the outward force exerted thereon by suture 104 and remains in place throughout the healing process. However, the reliability of suture anchor 103 depends on the material strength of the bone in which cylindrical hole 201 is formed. As long as the bone surrounding suture anchor 103 can withstand the outward force directed on the anchor by suture 104, suture anchor 103 will not be displaced.
It is known that for some patients the bone making up humeral head 102 forms a relatively weak base material for supporting suture anchors, since this portion of humerus 100 is relatively porous and soft. In addition, because the diameter 203 of cylindrical hole 201 is relatively large, typically 3 mm or greater, only a small number of suture anchors 103 can be installed in the appropriate region of humeral head 102, i.e., region 105, using this approach. A smaller number of suture anchors 103 results in higher forces on each suture anchor increasing the possibility that the suture anchor might be displaced out of the hole. Further, the formation of cylindrical holes 201, due to their relatively large diameter 203, can significantly weaken the mechanical strength of the anchoring bone material that surrounds suture anchors 103. Thus, adequate fixation of suture anchors 103 to the weaker bone material of humeral head 102 is problematic, and anchor displacement from the supporting bone is a common failure mechanism of suture anchors 103.
In addition, the use of suture anchors 103 limits the number of sutures securing rotator cuff tendon 101 to humeral head 102. This is due to the size constraint between suture anchors 103 and the region of humeral head 102 in which the anchors are placed. Fewer sutures provide a less robust connection between rotator cuff tendon 101 and humeral head 102. In addition, fewer sutures require the use of larger sutures, which have substantially larger suture and knot volumes. It is known that knots may act as sources of irritation and infection and that knot volume should be minimized, when possible. It is also known that, for a given surgical application, using more small-diameter sutures is generally preferable over fewer large-diameter sutures, since the latter case results in the largest total knot volume. This is because the knot volume of a suture is roughly proportional to the cube of the suture diameter.
Other suture anchors known in the art include devices that screw into cylindrical hole 201 in FIG. 2. Rather than relying on a rotating or “camming” action of the device to remain in place, as described above for suture anchor 103, a screw-in style device is held in place by contact between the external threads of the device and the bone surrounding cylindrical hole 201. This approach also relies on the mechanical strength of the bone surrounding cylindrical hole 201. A stronger mechanical connection between a suture anchoring device and the surrounding bone can be achieved by increasing the diameter of the anchoring device and its associated insertion hole. However, as described above regarding suture anchor 103, forming larger diameter holes in surface 202 of humeral head 102 further weakens the supporting bone and reduces the total number of anchors that can be installed in the desired location. This is particularly problematic for older patients with weaker bones.